This invention relates to a back light for a liquid crystal display (LCD).
In general, LCD is composed of a liquid crystal display element into which a liquid crystal having a quality of dielectric anisotropy is injected, and a light emitting means which projects a light from the outside of the liquid crystal display element.
Therefore, the above described LCD displays a letter or a number, those being designated, or other random pictures on the screen, using the quality of the light reflection of the liquid crystal differentiating in accordance with the change of the voltage applied from the outside.
Also, mini LCD which is used in articles like hand phones uses a back light retaining a number of light emitting diodes as a light emitting means, and the diodes are attached to lead frames and respectively installed in a mold part.
In such a case, according to the characteristics of the back light, the light emitting diodes are installed in the mold part in series or in a parallel form.
FIG. 3 illustrates the installation of the light emitting diodes in a parallel form. As shown in the drawing, the back light for LCD includes a mold part 1. A first lead frame 3 is installed in the mold part 1 and connected to a plus electrode of a power source. A plurality of light emitting diodes 5 are installed on the first lead frame 3 and each light emitting diode includes a chip 50. An anode electrode is arranged in the lower part of the chip and attached to the light emitting diode.
The back light further includes a second frame 7. The second frame 7 is installed in the mold part 1 in the opposite direction of the first frame 3. Further, the second frame 7 is connected to a minus electrode of the power source. The back light also includes a bonding wire 9. A cathode electrode 52 is arranged on the upper part of the chip 50 and connected to the second frame 7 with the bonding wire 9.
The conventional back light for LCD in which the light emitting diodes 5, as described above, are installed in a parallel form, is used in LCD of low voltage level when LCD comes into operation.
However, the back light for LCD like the above, namely the back light retaining the light emitting diodes installed in a parallel form, has a problem. That is, it becomes difficult to structurize LCD with a thin film on account of the enlarged size of the back light. In the attached drawings, this size is followed by a small letter d.
When in the back light, the light emitting diodes respectively having a fixed size have been installed in a parallel form, the size of the back light becomes enlarged in accordance with the increase in the volume of the mold part occupied by the light emitting diodes as well as the first and second lead frames since, on the inside of the mold part, the second lead frame is positioned on the upper part of the first lead frame.
As described above, the size of the conventional back light is determined by the size of the light emitting diodes as well as the size of the lead frames.